What is a computing system?
A computing system is any device that follows instructions to work with data: a laptop, phone, washing machine, car or smart watch.
- Input: data going in (keyboard, touch screen, microphone, camera, temperature sensor).
- Process: the CPU (central processing unit) follows instructions to work on the data.
- Output: results coming out (screen, speaker, printer, motor, LED).
- Storage: keeping data for later (SSD, hard disk, memory card, cloud).
Hardware is the physical parts you can touch. Software is the programs: the step-by-step instructions. Neither is useful without the other.
An embedded system is a small computer inside another device, built to do one job, like the controller in a microwave.
Layers of abstraction
Abstraction means hiding details that you do not need right now, so you can focus on what matters. A car driver uses the steering wheel and pedals without knowing how the engine works.
Computers are built in layers:
- User: you, tapping and typing.
- Applications (apps): browser, games, word processor.
- Operating system: manages everything and gives apps simple ways to use hardware.
- Hardware: CPU, memory, storage, input/output devices.
- Logic gates and circuits: tiny switches handling 1s and 0s.
Each layer talks only to the next one. An app says "save this file"; it does not need to know how the disk stores bits. This makes systems easier to build, fix and change: you can swap the hardware and the app still works.
Roles of the operating system
The operating system (OS) is the main system software. Examples: Windows, macOS, Linux, Android, iOS. Its jobs:
- Memory management: gives each program its own part of RAM and frees it when the program closes.
- Process management (multitasking): the CPU switches between programs very fast, giving each a short turn, so they seem to run at the same time.
- File management: stores files in folders, names them and controls who can open them.
- Device management: uses small programs called drivers to talk to printers, cameras and keyboards.
- User interface: a graphical interface (icons, windows, touch) or a command line.
- Security: logins, passwords, permissions and updates that fix weaknesses.
Logic gates: how hardware decides
Inside the hardware every signal is a bit: 1 (on, high voltage) or 0 (off). A logic gate takes one or two input bits and gives one output bit.
- AND: output 1 only if both inputs are 1.
- OR: output 1 if at least one input is 1.
- NOT: one input; flips it (1 â 0, 0 â 1).
- XOR: output 1 if the inputs are different.
- NAND: the opposite of AND.
A truth table lists every input and its output. For AND: 0,0 â 0; 0,1 â 0; 1,0 â 0; 1,1 â 1.
Example: a car warning beep = (door open) AND (engine on). Gates are joined into circuits that add numbers, store bits and run the CPU.
Designing usable devices and troubleshooting
Usability
A usable device is easy to learn, quick to use and hard to use wrongly. Designers think about who will use it (children, older people, people with disabilities), make buttons big and clear, give feedback (a beep, a light) and test with real users, then improve the design.
Projects that combine hardware and software
A simple project: a microcontroller board, a sensor (input), a program (process) and an LED or buzzer (output). Example: a plant-watering alarm that beeps when soil is dry. Plan â build â test â improve.
Systematic troubleshooting
- Describe the problem exactly: what happens, when, any error message.
- Check simple things first: power, cables, Wi-Fi, volume, restart.
- Change one thing at a time, so you know what fixed it.
- Test after each change.
- Record the problem and fix, and ask for help if needed.
Hardware or software? If the fault follows the part (try another keyboard), it is hardware. If it happens in only one app, or after an update, it is likely software.
Try it: trace the layers on your phone
- Open the camera app and take a photo. Write the I-P-O-S: input (camera sensor, tap), process (CPU makes the image), output (screen), storage (gallery).
- Find your phone's Settings â About. Note the OS name and version: that is the middle layer.
- Open Settings â Storage. See how the OS manages files for each app.
- In 3D step 6, fill in the full truth table for OR and XOR by flipping A and B. Predict before you tap.
Key formulas and definitions
- Input â Process â Output, with Storage
- Hardware = physical parts; software = instructions
- Layers: user â app â operating system â hardware â logic gates
- OS jobs: memory, processes, files, devices, interface, security
- AND: 1 only if both inputs are 1
- OR: 1 if at least one input is 1
- NOT: flips the input
- Troubleshoot: describe â simple checks â change one thing â test â record
Worked examples
1. Classify each as input, output or storage for a smart watch: heart-rate sensor, vibration motor, flash memory, touch screen.
Heart-rate sensor: input. Vibration motor: output. Flash memory: storage. Touch screen: both input (touch) and output (display).
2. A security light should switch on when it is dark AND movement is detected. Inputs: dark (1/0), motion (1/0). Which gate, and what is the output for dark = 1, motion = 0?
An AND gate. With dark = 1 and motion = 0, output = 0, so the light stays off.
3. Work out the output of NOT(A OR B) for A = 0, B = 1.
A OR B = 0 OR 1 = 1. NOT 1 = 0. Output = 0.
4. A printer prints nothing from one laptop but works from another. Using systematic troubleshooting, where is the fault likely and what would you check?
The printer hardware works (another laptop can print), so the fault is likely on the first laptop: check the cable or Wi-Fi connection, the selected printer, and the driver (reinstall or update it). Change one thing at a time and test after each.
Common mistakes
- Thinking the OS is an app like a game. It is system software that runs and manages all the apps.
- Confusing RAM (memory, temporary while working) with storage (keeps data when power is off).
- Mixing up AND and OR. AND needs both inputs 1; OR needs at least one.
- Changing many settings at once while troubleshooting, so you never know which change fixed it.